Stents are generally cylindrical shaped devices that are radially expandable to hold open a segment of a blood vessel or other anatomical lumen after implantation into the body lumen. Stents have been developed with coatings to deliver drugs or other therapeutic agents.
Stents are used in conjunction with balloon catheters in a variety of medical therapeutic applications including intravascular angioplasty. For example, a balloon catheter device is inflated during PTCA (percutaneous transluminal coronary angioplasty) to dilate a stenotic blood vessel. The stenosis may be the result of a lesion such as a plaque or thrombus. After inflation, the pressurized balloon exerts a compressive force on the lesion thereby increasing the inner diameter of the affected vessel. The increased interior vessel diameter facilitates improved blood flow. Soon after the procedure, however, a significant proportion of treated vessels re-narrow.
To prevent restenosis, short flexible cylinders, or stents, constructed of metal or various polymers are implanted within the vessel to maintain lumen size. The stents acts as a scaffold to support the lumen in an open position. Various configurations of stents include a cylindrical tube defined by a mesh, interconnected stents or like segments. Some exemplary stents are disclosed in U.S. Pat. No. 5,292,331 to Boneau, U.S. Pat. No. 6,090,127 to Globerman, U.S. Pat. No. 5,133,732 to Wiktor, U.S. Pat. No. 4,739,762 to Palmaz and U.S. Pat. No. 5,421,955 to Lau. Balloon-expandable stents are mounted on a collapsed balloon at a diameter smaller than when the stents are deployed. Stents can also be self-expanding, growing to a final diameter when deployed without mechanical assistance from a balloon or like device.
One problem in the manufacture of drug coated and/or drug eluting stents is the delicacy of the drugs. Many drugs used with stents degrade or lose biological activity when exposed to high temperatures. This has limited the number and type of drugs available for treatment of conditions such as inflammation and restenosis. One approach has been to apply or incorporate the drug at room temperature. Unfortunately, room temperature solutions of drug and polymer fail to adhere to the stent. The drug coming off the stent can migrate to undesirable locations in the body, can create uncertainty in the delivered dosage, and can contaminate personnel handling the stents. The drug can also come off during the manufacturing process.
Additionally, concern over the long-term effects of stents in the body has led to experimentation with bioabsorbable stents, i.e., stents that are absorbed by the body after deployment. Materials used for bioabsorbable stents have included bioabsorbable metals. Unfortunately, the materials used to date have failed to produce satisfactory results. A bioabsorbable stent needs to seal any dissection and provide scaffolding to prevent wall recoil until such scaffolding is no longer needed. A metal bioabsorbable stent such as one made of magnesium lasts a few weeks after deployment in a vessel, but should be present for several months to prevent wall recoil. With the stent gone prematurely, the vessel is reduced in diameter, making the treatment ineffective.
It would be desirable to have a system of and method for stent manufacture that would overcome the above disadvantages.